feeding depression after transfer to uncontaminated medium. Therefore, this persistent response could provide the basis for a feeding endpoint as part of a D. magna in situ bioassay, which could circumvent the difficulties of measuring feeding rates in the field mentioned above. The bioassay could consist of a period where animals would be placed in the field an exposed to contaminants(exposure), immediately ferred to clean medium where feeding rates could be measured under controlled conditions(after exposure). To be of use as an endpoint, postexposure feeding depress- sion would have to be demonstrable at concentrations below lethality, after exposure to a wide range of toxic substances with different modes of action. Therefore, the aim ofthis paper was to investigate the consistency and sensitivity of the post exposure feeding response under laboratory conditions and to develop standardized method for a D. magna postexposure feeding depression bioassay that could be adapted for use in the field at a later stage.